Conventional turbine housings for turbochargers are normally produced by casting, and thus designed taking account of a flow of liquid metal, which leads to an increase in the thickness of the entire housing and to a high heat capacity.
Thus, when an engine is started, the heat quantity of gas flowing through a turbine is absorbed by a turbine housing and the temperature of the gas decreases, which negatively affects a temperature increase of a medium at the downstream of the turbine. Accordingly, in recent years, sheet-metal turbine housings made of plate have been increasingly brought into use to reduce heat capacity of turbine housings.
Using a sheet-metal turbine housing results in a reduced thickness and thus in reduced heat capacity, and in addition, provides a smoother surface, which makes it possible to reduce friction loss and flow loss of exhaust gas, as compared to a casted turbine housing.
On the other hand, using sheet metal reduces strength of a structural body. Thus, to secure containment performance in response to burst of a rotor, for instance, it is necessary to take some measure, such as to increase the thickness of a housing. However, increasing the thickness contradicts the effect to reduce the heat capacity.
Patent Document 1 (JP2012-211544A), Patent Document 2 (JP2006-161573A), and Patent Document 3 (JP4269184B), for example, disclose a technique related to a sheet-metal turbine housing or a technique for ensuring containment performance in response to burst of a rotor.
Patent Document 1 discloses a sheet-metal turbine housing including a protector disposed along a scroll direction on an outer peripheral section of a scroll part and on an outer side in a radial direction of a rotation shaft of a turbine rotor, the protector being fixed to the scroll part.
Further, Patent Document 2 discloses a sheet-metal turbine housing of a double-tube structure, including a scroll part forming a scroll-shaped exhaust-gas channel and a cover part covering the scroll part via a predetermined adiabatic space.
Still further, Patent Document 3 discloses a double-shell shaped turbine housing including a housing of a scroll shape formed of sheet metal and an exterior shell surrounding the housing via a gap.